57 lines
1.5 KiB
C++
57 lines
1.5 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___ALGORITHM_SHIFT_LEFT_H
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#define _LIBCPP___ALGORITHM_SHIFT_LEFT_H
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#include <__algorithm/move.h>
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#include <__config>
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#include <__iterator/iterator_traits.h>
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#include <type_traits>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if _LIBCPP_STD_VER > 17
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template <class _ForwardIterator>
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inline _LIBCPP_INLINE_VISIBILITY constexpr
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_ForwardIterator
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shift_left(_ForwardIterator __first, _ForwardIterator __last,
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typename iterator_traits<_ForwardIterator>::difference_type __n)
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{
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if (__n == 0) {
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return __last;
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}
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_ForwardIterator __m = __first;
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if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) {
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if (__n >= __last - __first) {
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return __first;
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}
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__m += __n;
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} else {
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for (; __n > 0; --__n) {
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if (__m == __last) {
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return __first;
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}
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++__m;
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}
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}
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return _VSTD::move(__m, __last, __first);
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}
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#endif // _LIBCPP_STD_VER > 17
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ALGORITHM_SHIFT_LEFT_H
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